1. Field of the Disclosure
The present invention relates to a motor control circuit and method that determines mechanical rotor position and compensates for noise caused by unbalance loads.
2. Related Art
It is common to use a motor control circuit to control an electric motor. Typically, these control circuits use closed loop control techniques to provide speed and torque control for the motor. One example of such a control circuit is assignee International Rectifier Corporation's IRMCK343. The IRMCK343 is well known and detailed information regarding this circuit is available at irf.com. The IRMCK343 also uses assignee International Rectifier Corporation's well known Motor Control Engine (MCE™) technology, which is described in assignee's U.S. Pat. No. 7,166,982, the entire contents of which are incorporated by reference herein.
While such control circuits provide satisfactory results for most applications, when the motor is used to drive an unbalanced, or eccentric load, vibrations of the load typically result in noise being generated in the feedback signals used by the control circuit to control the motor. For example, when the motor is used to drive a single stroke or double stroke compressor, vibrations of the compressor resulting from the unbalanced nature of the load driven by the drive shaft of the motor, cause oscillations, or ripples, in the speed control loop commonly used by the control circuit for speed control. The oscillations are the result of abrupt variations in the load torque that result from the unbalanced nature of the load. It is undesirable to allow these oscillations in the feedback signals since these oscillations can result in control problems.
Accordingly, it would be desirable to provide a motor control circuit and method that avoids these problems.